1. Technical Field
This present disclosure generally relates to light sensitive electronic devices and, in particular, to a method and system of shielding electronic devices from light.
2. Description of the Related Art
Advances in the field of semiconductor wafer-level manufacturing have enabled wafer-level processing techniques to be applied to the manufacture of optical lenses and to bump thru-silicon via (TSV) sensor technology. One application of these advances is in the manufacture of a new generation of camera modules. Although camera modules produced by these new processes have the benefit of being compact in size, many do not effectively prevent stray light from entering the camera lens. Stray light that enters the camera modules through sidewalls negatively impacts image quality. Techniques exist in the art for preventing stray light from entering the camera module, however each has the negative consequences of raising the cost of the camera module or increasing the overall size of the camera module, or both.
For example, FIGS. 1A and 1B show a known plastic molded lens housing 10 configured to be arranged over a sensor module (not shown). The molded lens housing 10 includes a lens stack 12 that extends from an opening 18 in a back surface 20 to an opening 22 in a front surface 24. The opening 22 in the front surface 24 allows an image to be sensed by the sensor module when assembled with the housing 10. The sensor module may be on a rectangular substrate that is configured to fit within the opening 18. The molded lens housing 10 is thick black plastic that absorbs light and acts as the primary light shield of the camera module. A thickness 14 of walls 16 increases the overall size of final camera module and is limited by manufacturing constraints of molded plastic. The molded lens housing 10 is manufactured separately and then attached to the sensor module in a subsequent step. Additionally, if the molded lens housing 10 is used with a TSV die, careful design is required to ensure that the molded lens housing 10 fully covers the TSV die to prevent stray light from entering the camera module at an edge.
FIG. 2 is a cross-sectional view of a camera module 26 having a thin metal shield can 28 positioned on top and side surfaces 36 and 38. The camera module 26 includes an optical lens 27 having semi-transparent sidewalls 29. The camera module 26 is formed on a top surface 31 of a TSV die 30 that extends wider than the semi-transparent sidewalls 29. The shield can 28 is manufactured as a separate component from the optical lens 27 and attached with glue 32 on the top surface 36. The camera module 26 is then heated in an oven to cure the glue 32 and secure the shield can 28 on the camera module 26.
The shield can 28 extends down to a bottom surface 33 of the TSV 30 to seal the camera module 26 and optical lens 27 from light. Misalignment of the shield can 28 can allow light into the camera module 27. Also, an air gap 34 extends between side surfaces 38 of the semi-transparent sidewalls 29 and the shield can 28. The shield can 28 can be 100 microns in thickness, which with the air gap 34 makes the overall device larger in size. The shield can 28 increases a width of the camera module 26 by more than 0.5 millimeters. The manufacturing and assembly of the shield can 28 are expensive and increase the camera module's overall size.
FIG. 3 is a known camera module 40 that uses precut sheets of high-temperature black paper 39 adhered to outer walls 44 of the camera module 40. The black paper 39 is coated with a high-temperature adhesive on one side that securely attached the paper 39 to the outer walls 44. The walls 44 of the camera module 40 are substantially similar in width to the TSV die 30. If there are variations between the width of the walls and the die 30, the paper 39 is difficult to align accurately, which complicates automating the method. The paper 39 is also unreliable in its adhesion to the sides of the camera module. The paper is easily scratched, which allows stray light to interfere with the lens. Accordingly, this method is expensive to implement and cycle times are higher than for other light shielding assemblies.